Plants are constantly exposed to a variety of biotic (e.g., pathogen infection and insect herbivory) and abiotic (e.g., high or low temperature, drought, flood, anaerobic conditions and salinity) stresses. To survive these challenges, plants have developed elaborate mechanisms to perceive external signals and to manifest adaptive responses with proper physiological and morphological changes (Bohnert et al., 1995). Plants exposed to heat and/or low water or drought conditions typically have low yields of plant material, seeds, fruit and other edible products. Practically all agricultural regions are prone to drought due to climatic variation or socio-economic constraints on water resources. It would, therefore, be of great interest and importance to be able to identify genes that confer drought tolerance to thereby enable one to create transformed plants (such as crop plants) with improved ability to survive water limiting conditions.
Plants cannot grow without sufficient water. While nutrient availability plays a critical role in plant growth and development, these nutrients must be in aqueous form. In addition, many marginal growing regions may have an adequate nutrient supply, but without enough water to allow maintenance of plant turgor and membrane integrity, such lands cannot be maximally cultivated. Increased plant drought tolerance enables the production of higher yields from such lands and/or enables existing yields of crops to be obtained with lower water input. As a consequence, crops are produced more cost-effectively.
One of the major consequences of drought is the loss of water from the protoplasm, which leads to increased ion concentrations within the cell. At high concentrations ions such as chlorine and nitrate inhibit metabolic functions (Hartung et al (1998) Prog Bot 59:299-327).Eventually a “glassy state” results from cell water loss and the concentration of protoplasmic constituents. Here, the remaining cell liquid is highly viscous, which increases the chances of protein denaturation and membrane fusion due to abnormal molecular interactions (see: Hartung et al. (1998) Prog Bot 59:299-327 and Hoekstra et al. (2001) Trends Plant Sci 6:431-438).This indicates that the ability to maintain cell turgor and metabolism is genetically encoded.
In the field of agriculture and forestry efforts are constantly being made to produce plants with an increased growth potential in order to feed the ever-increasing world population and to guarantee the supply of reproducible raw materials. This is done conventionally through plant breeding. The breeding process is, however, both time-consuming and labor-intensive. Furthermore, appropriate breeding programs must be performed for each relevant plant species.
Availability and maintenance of a reproducible stream of food and feed has been a high priority throughout the history of human civilization and lies at the origin of agriculture. Specialists and researchers in the fields of agronomy science, agriculture, crop science, horticulture, and forest science are even today constantly striving to find and produce plants with an increased growth potential to feed an increasing world population and to guarantee a supply of reproducible raw materials. The robust level of research in these fields of science indicates the level of importance leaders in every geographic environment and climate around the world place on providing sustainable sources of food, feed and energy for the population.